1. Field of the Invention
The present invention relates to devices having female sockets adaptable for matably receiving a complementarily shaped male member. The invention has particular application to means for retaining the member in the socket.
2. Description of the Prior Art
Various types of rotatably drivable devices, such as drive sockets for wrenches and socket-head threaded fasteners, are provided with a female socket recess adapted for receiving a complementarily shaped male drive member. A typical form of such a drivable device has a polygonal socket recess formed in one end of the device coaxially with the axis of rotation. Various techniques have been used to facilitate retaining the drivable device on the associated driving tool or other drive member or, stated another way, to retain the driving tool or member in the socket recess. Various types of magnetic means have been used for this purpose.
Another technique is to so shape the socket recess and/or the drive member so as to provide an interference fit which will frictionally hold the parts together. Thus, for example, in my U.S. Pat. No. 4,970,922, there is disclosed a fluted driving tool which is adapted for engagement in a similarly shaped socket recess, the tool and socket recess having cooperating drive surfaces. The drive surfaces in the socket recess are substantially parallel to the axis of rotation while those on the drive member are given a slight helical twist about the axis of rotation so as to afford a wedge fit in the socket recess.
It has been considered desirable to provide a drivable device with a socket recess shaped such that, when used with a driving tool of standard shape, it will provide a retention fit. It is known to provide a socket-head screw with a hexagonal socket recess provided with a slight helical twist. Such an arrangement is disclosed in U.S. Pat. No. 2,538,350. However, that screw is specifically designed for use with a mating, helically twisted drive tool, and not with a standard drive tool. Furthermore, a helically twisted socket recess is very expensive to manufacture. Normally, female socket recesses are made by a forming or upsetting process wherein a forming tool is driven axially into the device to form the socket recess. In order to form a helically twisted socket recess, it is necessary to twist the forming tool during the forming operation, which requires the use of specialized tooling and equipment which is expensive to design and manufacture.